Machine for finishing gears and the like



Dec. 6, 1966 F` HURTH 3,289,536

MACHINE FOR FINISHING GEARS AND THE LIKE Filed June 9, 1964 4 Sheets-Sheet l #ingo 2 INVENTOR. FR l TZ H URT H /VZL/ L2.; L" (//r/ f,

ATTORNEY Dec. 6, 1966 F, HURTH MACHINE FOR FINISHING GEARS AND THE LIKE 4 Sheets-Sheet 2 Filed June 9, 1964 Vr www www.

INVENTOR. FR l TZ H U RT H m m A Dec. 6, 1966 F. HURTH MACHINE FOR FINISHING GEARS AND THE LIKE Filed June 9, 1964 4 Sheets-Sheet 5 INVENTOR. FR ITZ H U RTH ATTORNEY Dec. 6, 1966 F. HURTH 3,289,536

MACHINE FOR FINISHING GEARS AND THE LIKE Filed June 9, 1964 4 Sheets-Sheet 4.

n il 22%! l 7 INVENTOR. FRITZ HURTH ATTORNEY United States Patent 3,289,536 MACHINE FOR FINISHING GEARS AND THE LIKE Fritz Hurth, Grunwald, near Munich, Germany, assiguor to Carl Hurth Maschinenund Zahuradfabrik, Munich,

Germany Filed .lune 9, 1964, Ser. No. 373,741 Claims priority, application Germany, June 10, 1963, H 49,410; July 20, 1963, H 49,782 16 Claims. (Cl. 90-1.6)

The present invention relates to shaving, lapping, honing and similar gear finishing machines. More particularly, the invention relates to improvements in an apparatus which controls the operation of such machines and which is especially suited for use in various types of gear shaving machines. Still more particularly, the invention relates to a control apparatus for use in machines for finishing of gears and other types of toothed workpieces wherein the axis of a workpiece crosses in space the axis of a shaving, honing, lapping or similar tool.

It is an important object of the present invention to provide a gear finishing machine which is constructed and assembled in such a way that the various steps in the course of a shaving, lapping, honing or other operation are timed with utmost precision so that each of a series of consecutive workpieces may be treated to the same degree of precision finish.

Another object of the invention is to provide a pressure responsive control apparatus which may be utilized in my machine and which insures that the timing and/ or duration of one or more steps will be controlled with requisite accuracy to obtain a precision finished product.

An additional object of the invention is to provide a gear finishing machine wherein not only one `but two or more steps in a gear shaving, honing, lapping or similar operation may be controlled in response to a predetermined pressure between iixed and movable parts so that all sensitive elements of the machine are protected from damage or destruction.

A concomitant object of the invention is to provide a machine of the just outlined characteristics wherein the workpiece is disengaged from the tool in a fully automatic way and at such a speed that the finish of its Hanks is not destroyed during such disengagement and that the interval necessary for disengagement may be used to further improve the finish on the flanks of teeth on a freshly shaved, lapped or similarly treated workpiece.

Still another object of the invention is to provide a hydraulic, pneumatic, electrical or magnetic load cell which may be utilized in the improved control apparatus.

Another object of the invention is to provide a control apparatus for use in gear finishing machines, particularly in gear shaving machines, and to construct the control apparatus in such a way that it may be installed in many types of existing machines without necessitating substantial and costly alterations in the basic construction of such machines.

A further object of my invention is to provide `a control apparatus which is as advantageous in comparatively simple gear finishing machines in which the workpiece merely moves into and out of mesh with a tool or vice versa, as in rather complicated machines which -are used for crown shaving of simple or complex toothed workpieces.

Still another object of the invention is to provide a control apparatus of the above outlined characteristics which may be installed in gear finishing machines utilizing cutters in the form of gears, hobs or the like and which may be readily adjusted to be useful in connection with treatment of differently dimensioned and/r configurated workpieces.

3,289,536 Patented Dec. 6, 1966 With the above objects in view, one feature of the present invention resides in the provision of a machine for finishing gears and similar toothed workpieces which comprises a fixed holder secured to the frame of the machine and a movable holder which is arranged to travel toward and away from the fixed holder so that a workpiece mounted on one of the holders may be moved into and out of mesh with a tool on the other holder. The machine also comprises a feed for mov-ing the movable holder with reference to the fixed holder and a novel control apparatus which changes the condition of the feed in response to a predetermined pressure measured by a suitable hydraulic, pneumatic, piezoelectric, magneto-elastic or otherwise constructed load cell. The load cell may be mounted on a fixed part of the machine (for example, on the frame or on the fixed holder) and cooperates with an actuating or pressure transmitting device which is then mounted on a part that moves with or in response to movement of the movable holder to initiate a suitable impulse which controls the operation of the feed. For example, the impulse initiated by the load cell when the pressure between the teeth of a workpiece and a shaving tool reaches a predetermined magnitude may arrest or reverse the feed so that the shaving operation is completed. Alternatively, the load cell may initiate the generation of an impulse which causes a change in the rate of feed so that the movable holder moves at a higher or lesser speed in a direction toward or away from the fixed holder. It is also possible to construct the control apparatus in such a way that the load cell will initiate the generation of two or more impulses, always in response to a predetermined pressure which exists at a given stage of the gear finishing operation.

In one of its simplest forms, the load cell or an equivalent pressure responsive device may comprise an elongation ruler or the like which causes the generation of an impulse when it expands or contracts in response to a predetermined stress. Alternatively, the load cell may be any one of a series of known load cells including those known as carbon pressure gauges, capacitors with flexible plates, load cells based on lthe inverse magnetostrictive effect, and others.

The novel features which are considered as characteristic of the inventionare set forth in particular in the appended claims. The improved gear finishing machine itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be `bes-t understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. l is a diagrammatic side elevational view of a gear shaving machine which embodies one form of my invention, a portion of the frame and of the work holder being broken away;

FIG. 2 is a front elevational view of the machine with a portion of the work holder broken away;

FIG. 3 is a greatly enlarged sectional view of a detail in the machine of FIGS. 1 and 2 and illustrates a control circuit which produces impulses in response to tilting of a cam shaft when the pressure between the `tool and Workpiece reaches a predetermined magnitude;

FIG. 4 is a developed view of a cam face on a blocking cam which is used in the machine of FIGS. 1 and 2;

FIG. 5 in an enlarged sectional view of a detail in a machine similar to that of FIGS. 1 and 2 but provided with a different control circuit which produces impulses in response to pressure between the frame and the work holder;

FIG. 6 is a diagrammatic front elevational view of a modified gear shaving machine which embodies another form of my invention, .the front portion of the work holder being broken away and the control circuit being 4arranged to cooperate with a load cell mounted in one of the work engaging tailstocks;

FIG. 7 is an enlarged section through the tailstock and further illustrates the details of the control circuit which cooperates with the load cell; and

FIG. 8 is Ia fragmentary front elevational view of a machine similar to t-he one shown in FIG. 6 but utilizing ya slightly modied load cell which is mounted in the tool holder.

Referring to FIGS. 1 and 2, there ris show-n a gear finishing machine in the form of a gear shaving machine having a frame 10 of the knee-and-column type. The front face of the column in this frame is provided with vertical guides or ways 18 for a work slide 19 which comprises vertical guides in the form of dovetailed rails 20 `for a second slide 21. The slide 21 may be lixed to the work slide 19 in a series of positions by means not shown .in the drawings and carries a housing 40 for a turntable 41 which is rotatable about a vertical axis. The turntable is provided with horizontal ways for a third slide 42 which may be move-d back rand forth. The upper side of the Iturntable 41 supports a plate 43 for a tlitable table 44 which is adapted to rock about a horizontal pivot 43a when the machine is used for crown shaving of gears. Such tilting of the turntable is caused by an adjustable guide rod 45 in response to reciprocation of the horizontal slide 42 under the action of an electric motor 47 which transmits motion through a pair of spur gears 48, a pair of change gears 49, two pairs of bevel gears 50, 51 and a further pair of spur gears 52. One of the gears 52 rotates a horizontal spindle 53 which meshes with la spindle nut 54 provided at the underside of the slide 42.

A gear shaped shaving tool or cutter 15 is mounted in ya tool holder 55 which is rotatable with reference to the head of the frame 10 and which may be arrested in selected positions of adjustment so that its axis may cross in space with the axis of .a gear-shaped workpiece 26. The workpiece is held between the centers of two w-ork engaging tailstocks 24, which are mounted at the upper side of the table 44. If necessary, the tailstocks 24, 25 may be mounted on a second turntable which is then supported iby the table 44.

The frame 10 supports a rotary cam shaft 28 which carries a detachable blocking element in the form of a cam 27. 'Ilie cam shaft 28 is driven by an electric motor 29 through a variable-speed transmission 30 which drives a 'worm shaft 31. The worm on this worm shaft meshes with a worm wheel 32 on the cam shaft 28. The rear end portion of the cam shaft 28 carries lobes 33, 34 which cooperate with control switches 35, 36 to initiate or terminate certain operations of the shaving machine in a manner to be described later. It is clear that each lo'be may cooperate with two or more switches -and/or that the cam shaft 28 may carry a single lobe or three or more lobes. The tnansrnission may be of the infinitely variable type.

The work slide 19 supports a roller follower 37 which is arranged to rotate about a horizontal shaft 37a and to track the peripheral faceof the blocking cam 27. As clearly shown in FIG. 1, the blocking cam 27 will determine the minimum distance between the axes of the tool 15 and workpiece 26, ie., this cam Will insure that the extent to which `the teeth ofthe Iworkpiece penetrate into the spaces between the teeth of the tool is always the same regardless of the nature of the gear cutting operati-on which precedes the shaving operation. 'llhe roller follower 37 is biased by a'package of dished springs 38 which are arranged to operate between the base of which are removed from the flanks on the teeth of the` workpiece. As a r-ule, the shaving machine will be provided with means for regulating the .bias of the springs 38. For example, such regulating means may comprise a spindle 39 which is axially movably mounted in the base of the frame 10 fand acts upon the lowermost spring of the package 38. Means are provided for moving the spindle 39 vertically and for thereby changing the initial Lil and i2 are equal.

compression of the springs. It is clear that the springs 38 may be replaced by other biasing means, for example, by a hydraulic or pneumatic biasing device which is equipped with a suitable regulating valve to control the compression of entrapped fluid in :the same way as the spindle 39 may con-trol the compression of springs 38.

In accordance with la feature of my invention, the cam shaft 28 is mounted in such a way that it may tilt very slightly at -a point close to the blocking cam 27, for example, in the bearing deiined by -the front wall 10a of the column in the fname 10. The rear end portion of the shaft 28 is rotatable in a pressure transmit-ting housing 302 which is movable vertically in a rear wall 10b of the column and which serves to transmit pressure to a load cell 305. The cam shaf-t 28 is mounted in radial antifriction bearings 303 which are installed in the housing 302. The wall 10b accommodates two rows of rollers or balls 304 which reduce friction when the housing 302 moves up and down in response to minimal tilting of the cam shaft 28. The balls 304 `are mounted without any play or under some compression so as to prevent lateral woblbling of the cam shaft. If necessary, an adjustable wedge or the like may be provided to eliminate the cleanance between the housing 302 and wall 10b.

At a point below the underside of -the housing 302, there is provided the Iaforementioned pressure responsive load cell 305 which may be of any known construction. In the illustrated embodiment, the load cell is of the so-called magneto-elastic type which is biased on the inverse magnetostrictive effect and which comprises a magneto-elastic yoke 306 having recesses for coils 307. To complete the magnetic iield, the upper ends of the recesses are plugged by rings 308. The connection between the housing 302 and yoke 306 includes a cover member 309. A heat conductor 310 in the yoke 306 serves to maintain the temperature at a constan-t value. The load cell operates in the inductive principle whereby changes in inductivity result in response to a reduction in permeability such as will take place on elastic compression of the yoke 306 when the housing 302 transmits pressure subsequent to `tilting of the cam shaft 28. Changes in inductivity are utilized to produce impulses which are genera-ted by la control circuit 311 which is an amplifier circuit having an impulse generator 312. This circuit is connected to `a source 313 of electrical energy and further comprises a stabilizer 314, a iirst: resistance 315, Ia seco-nd resistance 316 which is of the: variable type and serves to adjust the sensitivity of the cincuit, and a transformer 317 having two secondary windings 318, 319. The winding 318 is connected in: circuit with the coils 307, and the winding 319 is con-- nected in circuit with a variable resistance 320 which: serves to calibrate the circuit 311. Two two-way recti- 'fiers 321, 322 serve to rectify and to balance the currents in the two cycles of the circuit 311. The difference in output voltage of the rectifiers 321, 322 influences the impulse generator 312.

In unstressed condition of the yoke 306, the currents The load upon the cell 305 will cause a difference in the currents and the generator 312 will produce an impulse which is used to cont-rol the operation of the feed for the workpiece 26. Stops 1321 are provided to limit the extent of downward movement of the housing 302, and the control circuit 311 preferably comprises a switch 1322 which is open when the, circuit is not to be used.

FIG. 4 illustrates the blocking cam 27 in a developed view. The peripheral face of this cam comprises sections 204a, 199, 204 and 208. The section 204g is of circular outline and its center of curvature is located on the lax-is of the cam shaft 28 so that the slide 19 is stationary when the follower 37 tracks the section 204a. The distance between the lines 201, 201' corresponds to the length of the cam face.

The machine of FIGS. l to 3 operates as follows:

At the start of a shaving operation, the axis of the follower 37 is located on the line 201 and the follower then abuts against the section 204a. The workpiece 26 is in loose mesh with the tool 15. The switch 1322 of the control circuit 311 is open so that the circuit is open, or, alternatively, the stops 1321 may be moved to such position that they prevent downward movement of the housing 302, i.e., the cam shaft 28 may be held against tilting. For example, one of the switches 35, 36 may initiate movement of stops 1321 to a locking position in which the stops prevent tilting of the cam shaft 28.

In the first step, the operator starts the motor 47 to reciprocate the slide 42 with the workpiece 26 and he simultaneously starts the motor (not shown) which rotates the tool 15 so that the tool compels the workpiece 26 to rotate therewith. The operator also starts the motor 29 which drives the cam shaft 28 through the intermediary of the transmission 30, worm shaft 31 and worm wheel 32. In the first stage, the motor 29 rotates rapidly and drives the blocking cam 27 so that the follower 37 begins to travel along an inclined section 199 of the cam face (see FIG. 4 which `shows the follower 37 in a position 202 corresponding to that when the follower begins to track the section 199). As the blocking cam 27 continues to rotate, the follower moves toward the position 203 of FIG. 4 `because it is biased by the springs 38, and the workpiece 26 is fed upwardly (arrow 210) so that its teeth penetrate deeper into the spaces between the teeth of the tool 15 whereby the two gears mesh without any clearance and the shaving operation begins when the follower 37 reaches the position 203. The section 199 of the cam face slopes inwardly toward the center of the cam shaft 28 so that the follower 37 (in the position 203) is separated from the blocking cam and the springs 38 then keep the teeth of the workpiece 26 in proper mesh with the teeth of the tool 15. Consequently, and since the `springs 38 generate a pressure which is necessary for removal of shavings, the teeth of the tool remove shavings from the flanks on the teeth of the workpiece while the blocking cam 27 continues to rotate until the section 204 of its cam face reaches a position just above the follower 37 which is then in a position 205 (see FIG. 4). The blocking cam 27 is then arrested by one of the lobes 33, 34 which close the corresponding switch 35 or 36, and the switch opens the circuit of the motor 29 or disconnects the transmission 30 so that the cam shaft 28 comes to a halt. However, and since the motor which drives the tool 15 continues to rotate, and also because the springs 38 continue to bias the workpiece 26 upwardly (by operating between the base of the frame and the work slide 19), the teeth of the tool continue to remove shavings while the follower 37 rises gradually from the position 205 to the position 206 in which it returns in engagement with the cam faces, i.e., with the section 204 on the peripheral face of the blocking cam 27.

At the time the tool removes shavings from the flanks of the workpiece 26, namely, while the follower 37 rises from the position 205 to t-he position 206, the switch 1322 is closed by a suitable trip mounted on the work slide 19 to complete the control circuit 311. Alternatively, and if the switch 1322 if normally closed, one of the switches 35, 36 may cause withdrawal of the stops 1321 so that the cam shaft 28 is free to tilt and to move the housing 302 downwardly into compressive engagement with the yoke 306 of the load cell 305. The load cell will cause the control circuit 311 to produce an impulse when the follower 37 rises to the position 206 of FIG. 4 and engages the section 204 of the face on the blocking cam 27. This will be readily understood because the follower is under the bias of springs 38 and exerts a pressure on the cam 27 whereby the latter causes the shaft 28 to tilt and to displace the housing 302 in a direction toward the cover member 309. The impulse produced by the generator 312 is used to start the motor 29 so that the carn shaft 28 begins to `rotate anew and the follower 37 begins to travel from the section 204 toward and along the outwardly inclined section 208 on the face of the yblocking cam 27. This means that the workpiece 26 is moved away from the tool 15. At the time the cam 27 is stationary and at the time the follower 37 travels from the position 206 to the position 207 of FIG. 4, the tool carries out the so-called smoothing or finishing operation when its teeth remove very thin shavings or merely roll along the flanks of the teeth on the workpiece. As a rule, the impulse sent by the generator 312 will cause the cam 27 to start rotating at a slow speed so that the tool will have enough time for the finishing operation. When the follower 37 reaches the position 207 of FIG. 4, one of the lobes 33, 34 closes the corresponding switch 35 or 35 and the motor 29 begins to rotate at increased speed to rapidly withdraw the workpiece 26 from mesh with the tool 15 and to return the work slide 19 to its initial position in which the shaved workpiece may be replaced by a fresh workpiece. The shaving operation is terminated when the follower 37 reaches the position 209, and the motor 29 is arrested by one of the switches 35, 36 when the axis of the follower is on the line 201.

The load cell 305 is a pressure responsive electromagnetic device in which the elastic deformation of the yoke 306 results in reduced permeability and thus in a change in inductivity of a current passing through the induction coils 308. This is known as the inverse magnetostrictive effect.

FIG. 5 illustrates a portion of a machine which is similar to that shown in FIGS. l and 2. The load cell 305 is replaced by a load cell 224 which is mounted in the work slide 19 and is compressed by the roller follower 37 when the latter reengages the face of the blocking cam 27. The shaft 37a of the follower 37 is mounted in a housing 222 which cannot rotate but is reciprocable vertically with reference to the work slide 19 (see the key 222a). The springs 38 act through a cupped retainer 223 which is recessed in the slide 19. The underside of the housing 222 is provided with a recess to accommodate the pressure responsive load cell 224 which is actually a capacitor adapted to alter the equilibrium in a bridge circuit 225. The capacitance of the capacitor 224 changes in response to changes in pressure transmitted by the retainer 223. The bridge circuit 225 further comprises a second variable capacitor 226 which is inserted in the same arm as the capacitor 224, two resistors 227, 228 in a second arm, a source 229 of electrical energy, and an impulse generator 230. The source 229 is connected in series with a switch 231 which may be operated (directly or indirectly) by one of the lobes 33, 34 shown in FIG. 1. Instead of using a variable capacitor 226, the bridge circuit 225 may comprise one or more variable resistances.

It is to be noted that the "bridge circuit 225 of FIG. 5 may be replaced by many types of equivalen-t circuits without in any way departing from the spirit of 4our invention. All that counts is to provide a highly sensitive control device which -may be adjusted with utmost accuracy so that it will respond to a predetermined pressure and will be in a position to determine with requisite exactness the timing and/or duration of one or more steps in a s-having, lapping, honing, burnishing or other gear treating operation. Thus, the `bridge circuit of FIG. 5 m-ay `be replaced by one known as ya quotient-difference circuit an-d many others. The impulse generator 230 will serve to start the cam shaft 28 when the follower 37 reaches a position corresponding to that shown at 206 in FIG. 4. The operative connection between the impulse generator 230 and the circuit of the motor 29 whic-h drives the cam shaft 2S is indicated schematically by an arrow 132.

The machine of FIG. operates as follows:

When the follower 37 is in positions corresponding to those shown at 37, 202 and 203 in FIG. 4, the switch 231 is open and the capacitor 224 is ineffective. When the follower 37 moves away from the face of the cam 27 (see the position 205 in FIG. 4), the switch 231 is closed so that the capacitor 224 is ready to operate. When the follower 37 rises to a position corresponding to that shown at 206 in FIG. 4 and returns in engagement with the face of the blocking cam 27, the pressure between the bearing 222 and retainer 223 increases and, as soon as such pressure reaches an exactly predetermined magnitude, the capacitance of the capacitor 224 changes in a well known manner to initiate the generation of an impulse which is sent from the generator 230 to the motor 29 of the cam shaft 28 so that the blocking cam 27 begins to rotate and causes the workpiece to move away from the tool. The operation then continues in the same way as described in connection with FIGS. 1-4. Thus, if the control apparatus of FIG. 5 or an analogous control device is used in the machine of FIG. 1, it replaces the structure of FIG. 3 and sends impulses to the motor 29. It is further to be understood that the machine of our invention may utilize hydraulic or pneumatic pressure responsive devices. Also, the machine which embodies our invention is equally useful for treatment of toothed Workpieces by tools other than a gear shaped tool. For example, the workpieces may be treated by a hob.

Referring to FIG. `6, there is shown a modified machine for .precision treatment of gears without transverse feed, i.e., the machine is equipped with means for merely moving the teeth of the workpiece into and out of mesh with the teeth of a tool, or vice versa. The machine is assumed t-o be used for shaving of external gears and comprises a frame 261 of the knee-and-column type, si-milar to the frame 10. The head of the frame 261 supports a rotary tool holder 262 for a gear-shaped shaving tool or cutter The motor which drives the tool 15 is of known construction and is not shown in FIG. 6. The front face of the column in the frame 261 is provided with vertical guides or ways 264 for a reciprocable work slide 263, i.e., the slide 263 is reciprocable in directions which are parallel with the axis about which the tool holder 262 may rotate. Means (not shown) are provided for releasably fixing the slide 263 in a selecte-d position.

The work slide 263 supports a horizontal pivot 266 for a tiltable work table 265 which carries two work engaging members in the form of tailstocks 267,268. The tailstocks support a gear-shaped workpiece 26' whose axis preferably crosses in space with .the axis of the tool 15. In the machine of FIG. `6, the workpiece 26 rotates when its teeth mesh with the teeth of the revolving tool. The extent to which the table 265 may be tilted about the axis of the pivot 266 is regulated by two adjusting screws 269, 270 which are mounted on the slide 263 and which normally allow for minimal tilting of the workpiece 26.

The tailstocks 267, 268 are provided with recesses to receive portions of two blocking elements 271, 271a which may be clamped in position by screws 272.

The feed which serves to move the work slide 263 along the ways 264 comprises a variable-speed transmission 280 whose output shaft drives a worm shaft 280a having -a worm which meshes with a worm wheel forming part of a rotary spindle nut 281. This nut is rotatable in the slide 263 but cannot move axially with respect thereto. The worm on the shaft 28051 is concealed by the nut 281, and this nut meshes with a vertical spindle 273. The transmission 230 is driven by a reversible electric motor 274 through the intermediary of a friction clutch 282. Alternatively, the nut 281 may be rotated by a manually operated mechanism including a hand wheel 275, .a face clutch 283 and a transmission including a train of gears 204. Of course, the clutch 233 is -inactive when the slide 263 is reciprocated by the motor 274, and the transmission 280 lis inactive when the nut 281 is rotated by the hand wheel 275. The transmission including the gears 234 may be of the infinitely variable type.

The minimum distance between the axes of the tool 15 and workpiece 26 will be determined by the dimensions and mounting of the blocking elements 271, 271a. If the sto-p faces 278, 279 on the toll holder 262 are located in a common horizontal plane and if the blocking elements are of identical dimensions and are mounted in the same way, the axis of the workpiece 26 will remain horizontal at the time the elements 271, 271e, respectively abut against the stop faces 273, 279. Such machine is suited for shaving or other treat-ment of spur gears and similar toothed workpieces. If the machine is to be converted for shaving or other treatment of bevel gears, one of the blocking elements 271, 27141 is replaced by a differently ldimensioned blocking element and the screws 269, 270 are adjusted to permit tilting of the table 265.

The left-hand tailstock 267 is of conventional construction and the conical tip of its center engages one end face of the shaft of the workpiece 26. The other tailstock 268 comprises a center 26861 which may yield to a predetermined vertical pressure and whose mounting is illustrated in FIG. 7. The tailstock 26S accommodates a pressure transmitting housing 401 which is movable in a direction at right angles to the axis of the workpiece 26 and is rigidly secured to the center 268g. This housing is mounted in antifriction bearings including two rows of balls 402. As a rule, the balls 402 will be inserted without play or even with a certain amount of compression to prevent any wobbling of the housing 401. If necessary, a wedge or the like may be employed to eliminate tolerances. Beneath the housing 401, there is provided a pressure responsive load cell which may be replaced by one of the hydraulic -or electrical type. In the illustrated embodiment, this load cell is again of the magneto-elastic type and includes `a magneto-elastic yoke 403 having recesses which receive 4coils 404. To complete the magnetic field, the upper ends of the recesses in the yoke 403 are plugged by rings 405. The operative connection between the yhousing 401 and yoke 403 comprises a cover member 406. The yoke 403 may accommodate a heat conductor 407 to insure -that the temperature remains constant in a manner well known in the art.

The load cell of FIG. 7 operates on the aforementioned principle that a change in inductance is caused by a change in permeability which is caused by elastic compression of the yoke 403. Such change in inductance (inverse magnetostrictive effect) is utilized to produce a suitable impulse in a control circuit 408 which includes an impulse generator 409. The circuit 403 is connected to a source 410 of electrical energy and includes a stabilizer 411, a rst resistor 412, a second resistor 413 of the variable type which serves as a device for regulating the sensitivity of the circuit, and a transformer 414. The secondary windings 415, 416 of the transformer 414 are respectively connected with the coils 404 and with a variable resistor 417 which serves as a means for calibrating the circuit 40S. Two two-way rectifiers 418, 419 serve to rectify and to balance the currents in the two cycles. The output voltage of the rectiiiers 418, 419 influences the impulse generator 409.

When the yoke 403 is not under compression, the currents i1 and i2 are equal. When the cell is under load, the difference between the two currents will cause the generator 409 to produce an impulse which will control the feed of the workpiece 26. Stops 420 are provided to arrest the housing 401 in a given position with reference to the load cell and/ or to prevent yielding of the center 268e at certain stages of the operation. The control circuit 408 further comprises a switch 421.

If desired, the load cell 403-406 may exert a back pressure which normally keeps the housing 401 in abutment with a stop face 422 in the tailstock 268. Such back pressure may be generated by suitable springs, bolts, screws or the like, not shown in the drawings. As stated above, the load cell of FIG. 7 constitutes but one form of control device for regulating the operation of the machine in response to a predetermined pressure between the teeth of the tool 15 and workpiece 26. Such control devices may operate on the principle that changes in pres* sure will cause changes in resistance, capacitance, inductance, permeability or another characteristic of an electric or magnetic system.

The machine of FIG. 6 operates as follows:

At the start of a shaving operation, the side 263 has been moved to a lower end position so that a fresh work piece 26 may be inserted between the tailstocks 267, 268. The screws 269, 270 are adjusted in such a way that they allow for slight tilting of the table 265 such as is necessary to allow for proper adjustment of the work holder (including the slide 263 and all parts carried thereby) in dependency on the dimensions and mounting of the blocking elements 271, 27161. The dimensions of the elements 271, 271a will depend on the desired minimum distance between the workpiece 26 and tool 15'.

To begin with the operation, the person in charge closes a main switch 423 to start the motor 274 and to begin with the feed of workpiece 26 toward and into mesh with the tool 15. The switch 421 remains open and the control circuit 408 is open. This circuit will be closed only when the pressure between the teeth of the workpiece 26 and tool 15 reaches a predetermined magnitude, .and such closing may be effected in a fully automatic way by causing the switch 421 to close in response to movement of the work slide 263 in a predetermined position, in response to movement of one of the blocking elements 271, 271e in abutment with the tool holder 262, or in another suitable way.

When the switch 421 is closed and when the center 268a of the tailstock 268 subjects the housing 401 to a given maximum pressure, the housing 401 transmits such pressure to the cover 406 and to the yoke 403 of the load cell. The impulse generator 409 then sends an impulse (see the conductors 408a in FIG. 6) to a relay 293. Such impulse induces the relay 293 to maintain its normally closed contacts 295 in closed position which means that the motor 274 continues to feed the work holder toward the tool holder 262. The feed is terminated when the blocking elements 271, 27161 respectively engage the stop faces 278, 279 on the tool holder 262. The motor which drives the tool 15 continues to rotate so that the teeth of the tool continue to mesh with the shaved teeth of the workpiece 26 whereby the tool performs a smoothing or finising step which may be called post-shaving with negligible removal of shavings or without any removal of shavings. Of course, as the teeth of the tool continue to treat the workpiece while the blocking elements 271, 271a abut against the stop faces 278, 279, the pressure between the tool and workpiece begins to decrease and, as soon as the pressure decreases to a predetermined value, the circuit 408 sends another impulse which causes the relay 293 to open the normally closed contacts 295 and to simultaneously close a set of normally open contacts 296 which cause the motor 274 to reverse the direction of its movement and to lower the finished workpiece 26 away from the tool 15. If necessary, the relay 293 may react immediately, as soon as it receives an impulse through the conductors 208g, or this relay may be a time-lag relay and reverses the motor 274 after elapse of a predetermined interval of time which is necessary for satisfactory smoothing of flanks on the teeth of the workpiece. When the slide 263 returns to l0 its original position (i.e., to the lower end. position), it opens the main switch 423 in a manner not shown in the drawings so that the motor 274 is arrested and the workpiece 26 is ready to be replaced by a fresh workpiece.

The contacts 295, 296 return to their original positions and the motor 274 is ready to feed the slide 263 upwardly as soon as the main switch 423 is closed.

It goes without saying that the improved control system is equally useful in other types of gear shaving, lapping, honing and similar machines. For example, and as explained in connection with FIGS. l to 4, the situation is analogous if the workpiece must reciprocate and is tilted back and forth while its teeth mesh with the teeth of the tool. Such movements of the workpiece are necessary 1n crown shaving of gears. It is equally obvious that the load cell may be mounted in another part of the machine, for example, so as to respond to pressure exerted by the table 265, by the slide 263 or by another part which is mounted on the work holder. The pivot 266 may be transferred to one end of the work table 265 and the other end of this table may rest on a suitable load cell. In such modified machine, the blocking elements 271, 271:1 must be mounted directly on the work slide 263 or on another part which is rigid with the work slide. It is further clear that the invention may be practiced m machines wherein the work holder is reeiprocated by means other than an electric motor. For example, the machine may be reciprocated by a hydraulic or pneumatic feed device.

Finally, it is equally possible to mount the load cell of FIG. 7 in such `a way that it may rotate about the center 26861 so that this cell may take up stresses which act in a direction other than vertically downwardly. In other words, the load cell may be used to respond to pressures which act in directions other than the direction in which the work slide 263 moves along the ways 264.

In the machine of FIGS. 6 and 7, the load cell bccomes operative and initiates the generation of an impulse when the pressure between the tool 1S and workpiece 26 begins to decrease. This will be readily understood by considering that the relay 293 opens its contacts 295 and closes the contacts 296 `with a certain delay, i.e., in delayed response to an impulse received from the circuit 40S at the time when the pressure between the housing 401 and yoke 403 reaches a maximum value. Consequently, and depending on the setting of the relay 293, the feed will reverse the direction of .movement of the work slide 263 with a delay which is sufficient to allow for completion of the finishing step. In other words, the work slide 263 should not be reversed at the time when the pressure between the workpiece 26 and tool 15 reaches a maximum value but rather with a certain delay which is necessary for completion of the finishing step.

FIG. 8 illustrates a modification of the machine shown in FIGS. 6 and 7. The load cell is placed in the path of the blocking element 271a and is mounted in the tool holder 262. This load cell operates on the principle known as the piezoelectric effect and controls the operation of the reversible feed motor 274. The load cell comprises one but preferably two or more stacked piezo crystals consisting of quartz, turmaline, phosphate, titanate or tartrate. In the embodiment of FIG. 8, two crystals 285, 286 are mounted in the tool holder 262 just above the stop face 279, and a portion 287 of the tool holder is grounded, as at 287e. An intermediate electrode 285:1 between the crystals 285, 286 is connected. with a conductor leading to the grid G of an amplifier tube 289` The cathode K is grounded at 291, together with one pole of a source 290 of electrical energy. The anode A is connected with a conductor 292 leading to one end of the winding in the relay 293. A further conductor 294 connects the other end of the winding with the second pole of the source 290. The relay 293 is a time-lag relay and controls the direction in which the motor 274 rotates.

The normally closed contacts 295 complete the circuit of the motor 274 in such a way that the workpiece 26 is fed upwardly toward the tool and the normally open contacts 2% will close when the motor 274 is to be reversed so as to move the workpiece away from the tool. The arrow a indicates the direction of automatic return movement of the contacts, and the arrow b indicates the direction of delayed action.

The operation of the just described machine is analogous to that of the machine shown in FIGS. 6 and 7. When the motor 274 feeds the workpiece 26 upwardly, the contacts 295 are closed but the contacts 296 are open. As soon as the blocking element 27M strikes against the crystal 28d, the load cell is compressed and produces a current whereby the amliier 289 sends an impulse (conductor 292) which causes energization of the relay 2% after a period of time necessary for completion of the finishing step. The relay 293 then opens the contacts 295 and closes the contacts 296 so that the feed motor 274 runs in reverse and moves the finished workpiece 26 away from the tool 15.

The friction clutch 282 (see FIG. 6) takes up the shock when the blocking element 271:1 reaches the crystal 286. Thus, the clutch 282 may determine the maximum pressure between the blocking elements 271 (see FIG. 6), 271a on the one hand and the tool holder 262 on the other hand to thereby protect the load cell from excessive stresses. The tool holder is fixed to and may be considered to constitute a part of the frame when the machine is in use.

Without further analysis, the foregoingy will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications `without omitting features which fairly constitute essential characteristics of the generic and specic aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a machine for finishing gears and similar toothed workpieces, in combination, frame means; movable holder means, one of said means being arranged to support a material removing tool and the other of said means being arranged to support a workpiece; a feed for moving said holder means with reference to said frame means so as to bring the tool into and out of material removing engagement with a workpiece so that the tool and the workpiece can exert against each other a pressure which decreases in response to removal of material from the workpiece; a blocking element mounted on one of said means and arranged to limit the extent of movement of said holder means with reference to said frame means and to thus determine the minimum distance between the workpiece and the tool; and a control apparatus comprising a pressure responsive device mounted on one of said means and constructed to initiate the generation of an impulse in response to a predetermined pressure thereon corresponding to a minimum pressure between the tool and the workpiece, a pressure transmitting member mounted on the other of said means and arranged to transmit said predetermined pressure to said device in a selected position of said holder means when the pressure between the tool and the workpiece equals said minimum pressure, and an operative connection between said device and said feed for changing the condition of said feed in response to such predetermined pressure upon said device so that the feed then disengages the tool from the workpiece.

2. In a machine for finishing gears and similar toothed workpieces, in combination, frame means; movable holder means, one of said means 'being arranged to support a tool and the other of said means being arranged to support a workpiece; a feed for moving said holder means with reference to said frame means so as to bring a workpiece into and out of engagement with the tool; a blocking element mounted on one of said means and arranged to limit the extent of movement of said holder means with reference to said frame means so as to determine the minimum distance between the workpiece and the tool; a pressure responsive device constructed to initiate the generation of an impulse in response to a predetermined pressure thereon, said device being arranged to undergo compression which increases with diminishing distance between the tool and the workpiece; and an operative connection between said device and said feed for changing the condition of said feed in response to such predetermined pressure upon said device so that the feed then disengages the tool from the workpiece.

3. A combination as set forth in claim 2, wherein said pressure responsive device is a load cell and wherein said operative connection sends impulses to a motor forming part of said feed.

4. A combination as set forth in claim 3, wherein said load cell comprises a magnetoelastic yoke whose permeability changes in response to compression, coil means in said yoke, and a cover member arranged to compress said yoke in response to pressure transmitted by said blocking element, said connection comprising an electric circuit arranged to send impulses on changes in permeability of said yoke.

5. A combination as set forth in claim 3, wherein said blocking element is mounted on said holder means and said load cell is provided on said frame means in the path of movement of said blocking element.

6. A combination as set forth in claim 3, wherein said load cell is arranged to operate on the piezoelectric principle.

7. A combination as set forth in claim 3, wherein said load cell is an electrical load cell.

8. In a machine for finishing gears and similar toothed workpieces, in combination, frame means; movable holder means, one of said means being arranged to support a tool and the other of said means being arranged to support a workpiece; a feed for moving said holder means with reference to said frame means so as to bring a workpiece into and out of engagement with the tool; and a control apparatus comprising a rotary blocking cam mounted in said frame means, a follower reciprocably mounted in said holder means and arranged to track said cam, biasing means for normally maintaining said follower in engagement with said cam, said biasing means being disposed between said frame means and said holder means, a variable capacitor disposed between said follower and said frame means and arranged to change its capacitance in response to a predetermined pressure between said follower and said holder means under the action of said biasing means, and an operative connection between said capacitor and said feed for changing the condition of said feed in response to such predetermined pressure upon said capacitor.

9. A combination as set forth in claim 8, wherein said operative connection comprises a bridge circuit and wherein said feed comprises a reversible electric motor which is reversed in response to said predetermined pressure upon said capacitor.

10. In a machine for finishing gears and similar toothed workpieces, in combination, frame means; movable holder means, one of said means being arranged to support a tool and the other of said means being arranged to support a workpiece; a reversible feed for moving said holder means with reference to said frame means so as to bring a workpiece into and out of engagement with the tool; and a control apparatus comprising a blocking element mounted on one of said means and arranged to abut against a portion of the other of said means in response to movement of said holder means in a direction to advance the workpiece into engagement with the tool, a pressure responsive device mounted on one of said means and constructed to initiate the generation of an impulse in response to a predetermined pressure thereon, a pressure transmitting member on the other of said means for subjecting said device to such predetermined pressure when said blocking element abuts, and an operative connection for reversing said feed with a predetermined delay in response to said predetermined pressure upon said device so that the feed disengages the tool from the workpiece in response to elapse of such predetermined delay.

11. A combination as set forth in claim 10, wherein said pressure responsive device is an electric load cell and wherein said operative connection comprise-s an electric circuit including amplifier means and an impulse generator for producing impulses on transmission of said predetermined pressure to said load cell.

12. A combination a-s set forth in claim 11, wherein said operative connection comprises a time-lag relay and wherein said feed comprises a re-versible electric motor connected in circuit with said relay.

13. In a machine for finishing -gears and similar toothed workpieces, in combination, frame means; movable holder means, one of said means being arrange-d to support a tool and the other of said means being arranged to support a workpiece; a feed including a motor for moving said holder means with reference to said frame means so as to bring a workpiece into `and out of engagement with the tool; a rotary cam; a tiltable shaft connected with said cam and rotatably mounted in said frame means, said cam being arranged to limit the extent of movement of said holder means with reference to said fra-me means so as to determine the minimum distance between the Workpiece and the tool; a load cell constructed to initiate the generation of an impulse in response to a predetermined pressure thereon; a housing mounted on said .shaft and arranged to press against said load cell in response to tilting of said shaft, sai-d load cell being arranged to undergo compression transmitted by said housing; and an operative connection between said loa-d cell and said feed for sending an impulse to said motor in response to said predetermined pressure Iupon said load cell.

14. In a machine Ifor finishing gears and similar toothed workpieces, in combination, frame means; movable holder means, one of -said means being arranged to support a tool and the other of said -means being arranged to support a workpiece; a reversible feed for moving said holder means with reference to said `frame means so as -to bring a workpiece 4into and out of engagement with the tool; and a control apparatus comprising a yblocking element mounted on one of said means and arranged to abut against a portion of the other of said means in response to movement of said holder means in a direction to advance the workpiece into engagement with the tool, a load cell mounted on one of said means and constructed to initiate the generation of an impulse in response `to a predetermined pressure thereon, a pressure transmitting member on the other of said means for subjecting said load cell to such predetermined pressure when said blocking element abuts, and an operative connection for reversing said feed with a predetermined delay `in response to said predetermined pressure upon said load cell at a time when the pressure between the tool and the workpiece decreases.

15. In a machine for finishing gears and similar toothed workpieces, in combination, frame means; -movable holder means including a tailstock, one of said means being arranged to support a tool and the other of said means being arranged to support a workpiece; a reversible feed for moving said holder means with reference to said frame means so as to bring a workpiece into and out of engagement with the tool; and a control apparatus comprising a -blocking element mounted on one of said means .and arranged to abut against a portion of the other of said means in response to movement of said holder means in a direction to advan-ce the workpiece into engagement with the tool, a pressure responsive device mounted on said frame means and constructed to initiate the generation of an impulse in response to a predetermined pressure thereon, a pressure transmitting member constituted by a portion of said tailstock for subjecting said device to each predetermined pressure when said blocking element abuts, and an operative connection for reversing said feed with a predetermined delay in response to said predetermined pressure upon said device.

16. A combination as set forth in claim 15, wherein said pressure responsive device is mounted in said tailstock and wherein said portion of said tailstock is a center.

References Cited by the Examiner UNITED STATES PATENTS 2,978,689 4/1961 Tech et al. 77-32.7 X 2,982,899 5/1961 Rappaport et al. 318-39 X FOREIGN PATENTS 1,123,183 ll/l959 Germany.

ANDREW R. JUHASZ, Primary Examiner., 

1. IN A MACHINE FOR FINISHING GEARS AND SIMILAR TOOTHED WORKPIECES, IN COMBINATION, FRAME MEANS; MOVABLE HOLDER MEANS, ONE OF SAID MEANS BEING ARRANGED TO SUPPORT A MATERIAL REMOVING TOOL AND THE OTHER OF SAID MEANS BEING ARRANGED TO SUPPORT A WORKPIECE; A FEED FOR MOVING SAID HOLDER MEANS WITH REFERENCE TO SAID FRAME MEANS SO AS TO BRING THE TOOL INTO AND OUT OF MATERIAL REMOVING ENGAGEMENT WITH A WORKPIECE SO THAT THE TOOL AND THE WORKPIECE CAN EXERT AGAINST EACH OTHER A PRESSURE WHICH DECREASES IN RESPONSE TO REMOVAL OF MATERIAL FROM THE WORKPIECE; A BLOCKING ELEMENT MOUNTED ON ONE OF SAID MEANS AND ARRANGED TO LIMIT THE EVENT OF MOVEMENT OF SAID HOLDER MEANS WITH REFERENCE TO SAID FRAME MEANS AND TO THUS DETERMINE THE MINIMUM DISTANCE BETWEEN THE WORKPIECE AND THE TOOL; AND A CONTROL APPARATUS COMPRISING A PRESSURE RESPONSIVE DEVICE MOUNTED ON ONE OF SAID MEANS AND CONSTRUCTED TO INITIATE THE GENERATION OF AN IMPULSE IN RESPONSE TO A PREDETERMINED PRESSURE 